The transport of virulence factors from bacterium to the eukaryotic host cell has emerged as a fundamental strategy in pathogenesis. Several relevant Gram-negative pathogens use type IV secretion systems (T4SS) for 'effector'protein translocation. Coxiella burnetii, a Category B select agent and the causative agent of 'Q'fever is an obligate intracellular vacuolar parasite in vertebrates. After internalization by phagocytes, C.burnetii remodels its vacuole to replicate in a harsh phagolysosomal compartment, likely attributable to the translocation of effector proteins by a T4SS. Due to its obligate intracellular lifestyle, genetic manipulation of C.burnetii remains severely limited. Genomic information revealed however that C.burnetii harbors the genes encoding a T4SS found in Legionella pneumophila called Dot/Icm. Recent studies indicated that expression of C.burnetii (Cb) homologs of the dot/icm components IcmS and IcmW could complement intracellular growth defects of L.pneumophila (Lp) icmS or icmW mutants. We have established that IcmS and IcmW form a complex in the Legionella cytoplasm, and are important for early stages of substrate recognition. The goal of this study is to use L.pneumophila as a surrogate host for the characterization of specific secretion determinants of recently identified effector proteins from C.burnetii. Using molecular, genetic, and biochemical strategies, we will determine secretion signal signatures on Coxiella effector proteins, and define Cb IcmSW binding sites on Cb effectors. Determination of consensus secretion determinants will be applied to systematic computational approaches through the development of new search algorithms to identify novel effector proteins harbored on the C.burnetii genome. Outcomes from these studies will provide novel targets for antimicrobial development to combat critical stages of effector protein recognition and transport by the T4SS. PUBLIC HEALTH RELEVANCE: The Q fever bacterium Coxiella burnetii is an obligate intracellular pathogen whose lifestyle has impeded the development of reliable genetic tractability. We are using Legionella pneumophila, a related bacterium with pathogenic strategies predicted to be conserved, to identify and characterize critical transport determinants on virulence factors. This work will lead to the identification of a new catalog of virulence factors associated with establishment of Q fever, and provide novel targets for antimicrobial development